U.S. patent number 9,276,675 [Application Number 12/022,443] was granted by the patent office on 2016-03-01 for apparatus and method for transferring an optical signal in a wireless visible light communication system.
This patent grant is currently assigned to Samsung Electronics Co., Ltd.. The grantee listed for this patent is Jong-Hoon Ann, Jae-Seung Son, Eun-Tae Won. Invention is credited to Jong-Hoon Ann, Jae-Seung Son, Eun-Tae Won.
United States Patent |
9,276,675 |
Son , et al. |
March 1, 2016 |
Apparatus and method for transferring an optical signal in a
wireless visible light communication system
Abstract
A wireless visible light communication system is provided. The
system includes optical transmitters and optical receivers for
receiving optical signals, wherein each of the optical transmitters
includes a first light source for generating an optical signal, and
at least one light source capable of generating light which has a
color equal to that of the optical signal, and has a wavelength
different from that of the optical signal.
Inventors: |
Son; Jae-Seung (Suwon-si,
KR), Ann; Jong-Hoon (Suwon-si, KR), Won;
Eun-Tae (Seoul, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Son; Jae-Seung
Ann; Jong-Hoon
Won; Eun-Tae |
Suwon-si
Suwon-si
Seoul |
N/A
N/A
N/A |
KR
KR
KR |
|
|
Assignee: |
Samsung Electronics Co., Ltd.
(Suwon-si, KR)
|
Family
ID: |
40088344 |
Appl.
No.: |
12/022,443 |
Filed: |
January 30, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080298811 A1 |
Dec 4, 2008 |
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Foreign Application Priority Data
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May 30, 2007 [KR] |
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10-2007-52651 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B
10/116 (20130101); H04B 10/1149 (20130101) |
Current International
Class: |
H04J
14/02 (20060101); H04B 10/116 (20130101); H04B
10/114 (20130101) |
Field of
Search: |
;398/172 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2004-193908 |
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Jul 2004 |
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JP |
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2006-262458 |
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Sep 2006 |
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JP |
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10-2000-0025312 |
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May 2000 |
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KR |
|
WO 2006/033263 |
|
Mar 2006 |
|
WO |
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10-2006-0095495 |
|
Aug 2006 |
|
WO |
|
Other References
Wikipedia/color, retrieved Aug. 5, 2014, p. 1. cited by examiner
.
Kim et al., "Reduction of Cross-Gain Modulation in the
Semiconductor Optical Amplifier by Using Wavelength Modulated
Signal", IEEE Photonics Technology Letters, vol. 12, No. 10, Oct.
2000. cited by examiner.
|
Primary Examiner: Li; Shi K
Attorney, Agent or Firm: Jefferson IP Law, LLP
Claims
What is claimed is:
1. A wireless visible light communication system comprising: a
controller configured to control output powers of a plurality of
optical transmitters configured to transmit optical signals to a
plurality of optical receivers corresponding to the plurality of
optical transmitters, respectively, wherein each of the plurality
of optical transmitters comprises: a first light source configured
to generate a first optical signal, having a first wavelength in
the visible light spectrum, for transmitting data; and a second
light source configured to generate a second optical signal, having
a second wavelength in the visible light spectrum, the second
wavelength being different from and a substantially similar color
as the first wavelength and having a wavelength approximately 40-50
nm different from that of the first wavelength, wherein the
plurality of optical transmitters generate first optical signals
having mutually different colors, wherein each of the plurality of
optical receivers is configured to receive the first optical signal
from among the first and second optical signals outputted from a
corresponding one of the plurality of optical transmitters, wherein
a second amplitude pattern of the second optical signal has a shape
obtained by inverting a first amplitude pattern of the first
optical signal with respect to a reference value, and wherein each
of the plurality of optical receivers is configured to detect a bit
stream of logical ones and zeros from the first optical signal
based on the reference value.
2. The system of claim 1, wherein the different colors comprise
red, blue, and green.
3. The system of claim 1, wherein said each of the plurality of
optical transmitters further comprises an external modulator for
modulating the first optical signal generated by the first light
source.
4. The system of claim 1, wherein each of the plurality of the
optical receivers comprises: a wavelength selective filter for
selectively transmitting an optical signal which is generated from
the first light source and has a corresponding wavelength; a
photoelectric converter for converting an optical signal
transmitted through the wavelength selective filter into an
electrical signal; and a data detector for detecting data from the
electrical signal converted by the photoelectric converter.
5. The system of claim 1, wherein the first and second light
sources of each optical transmitter use a complementary modulation
scheme such that a sum of amplitudes of the first and second
optical signals is maintained to be a constant predetermined value,
wherein the controller controls powers of the optical transmitters
by adjusting a ratio of powers of the light sources according to
their respective colors, and wherein the wavelengths and output
powers are selected and controlled so as to uniformly maintain
emitted light in a constant natural light state.
Description
PRIORITY
This application claims the benefit under 35 U.S.C. .sctn.119(a) of
a Korean patent application filed in the Korean Industrial Property
Office on May 30, 2007 and assigned Serial No. 2007-52651, the
entire disclosure of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical communication system.
More particularly, the present invention relates to a wireless
visible light communication system.
2. Description of the Related Art
The term "optical communication" refers to a communication system
for transmitting a data-modulated optical signal through an optical
fiber. A benefit of optical communication is that it may be used to
transmit a large amount of data at a high speed. Optical
communication systems may be classified into a wavelength division
multiplexing scheme, a time division multiplexing scheme, a
sub-carrier multiplexing scheme, etc. according to an optical
signal transmission scheme. The wavelength division multiplexing
scheme uses rays of light having different wavelengths as carriers
for modulating data.
The wavelength division multiplexing scheme is a type of optical
communication method for transmitting optical signals. The optical
signals are data modulated into channels (i.e., light) having
different wavelengths, through optical lines or the like. Since the
wavelength division multiplexing scheme can transmit a plurality of
optical signals through a single optical line, the wavelength
division multiplexing scheme is an optical communication method
suitable for transmission of a large amount of data at a high
speed. Moreover, an optical communication system employing the
wavelength division multiplexing scheme can transmit different
types of data (e.g., Internet data, synchronous optical network
(SONET) data, asynchronous transfer mode (ATM) data, etc.) through
one optical line.
The wavelength division multiplexing scheme makes it easier to
select bands according to wavelengths as compared to the frequency
modulation and time division schemes. Therefore, the wavelength
division multiplexing scheme can also be applied to wireless
optical communication systems. However, the wireless visible light
communication system may be restricted to indoor use or ultra short
range communication because the wireless visible light
communication system uses light as a carrier.
The wireless visible light communication may use light sources
capable of generating white light as optical transmitters, or may
user light sources capable of generating light of a wavelength
which is invisible to the human eye (e.g., infrared ray, etc.).
When the wireless visible light communication system is applied in
an indoor environment, optical signals generated from the light
sources may additionally function as illumination, and light
sources of three colors (red, blue and green) may be used to
respectively generate optical signals to be used as carriers so
that the optical signals can be at substantially the same state as
natural light.
FIG. 1 is a block diagram schematically illustrating a
configuration of a conventional wireless visible light
communication system. A wireless visible light communication system
100 is a type of optical communication system which uses optical
signals data-modulated using light in a visible wavelength band as
a carrier. The wireless visible light communication system 100
includes optical transmitters 111, 112 and 113 capable of
generating optical signals 101, 102 and 103 having different
colors, and optical receivers 121, 122 and 123 for detecting the
optical signals 101, 102 and 103 generated from the optical
transmitters 111 to 113.
Each of the optical transmitters 111 to 113 includes light sources
capable of generating light having mutually different colors, and
may either further include an external modulator for modulating
data, or may be configured in such a manner as to directly modulate
data using the light sources. Since the wireless visible light
communication system uses light in a visible wavelength band, which
is visible to the human eye, as a carrier, it is necessary to
transmit optical signals in the natural light state so as to
minimize fatigue of the user. Accordingly, in an exemplary
implementation, the optical transmitters 111 to 113 may be
configured with light sources capable of generating three primary
colors (red, blue and green) which are mutually different.
The optical receivers 121 to 123 include photoelectric converters
121a to 123a for converting input optical signals at corresponding
wavelengths into electrical signals, and data detectors 121b to
123b for detecting data from the electrical signals,
respectively.
Photo diodes or phototransistors may be used as the photoelectric
converters 121a to 123a. In order to detect an optical signal at a
corresponding wavelength, a wavelength selective filter (or a band
pass filter or optical filter) for selectively transmitting only
the optical signal at a corresponding wavelength from one of the
received optical signals may be installed at the front position
through which the photoelectric converters 121a to 123a receive the
optical signals.
FIG. 2 is a graph illustrating a spectrum of an optical wavelength
band used in a conventional wireless visible light communication
system. Referring to FIG. 2, the graph illustrates powers of rays
of light according to colors (i.e. green, blue and red).
Accordingly, it can be understood that rays of light having colors
may have different powers depending on wavelengths.
Although the wireless visible light communication system using
light in a visible wavelength band is mainly used in an indoor
environment, the wireless visible light communication system has a
problem in that it is difficult to produce and maintain light in a
uniform state of natural light (white light) due to the
characteristic of colored light having different powers depending
on wavelengths.
SUMMARY OF THE INVENTION
An aspect of the present invention is to address the
above-mentioned problems and/or disadvantages and to provide at
least the advantages described below. Accordingly, an aspect of the
present invention is to provide a wireless visible light
communication system which can uniformly maintain light in a
natural light state while using light in a visible wavelength
band.
In accordance with an aspect of the present invention, a wireless
visible light communication system is provided. The system includes
a plurality of optical transmitters capable of generating optical
signals having different colors, and a plurality of optical
receivers capable of detecting an optical signal which has a
corresponding wavelength from one of the optical signals generated
by the plurality of optical transmitters, wherein each of the
optical transmitters includes a first light source for generating a
data-modulated optical signal, and at least one second light source
for generating light which has a color equal to that of the optical
signal modulated by the first light source, and has a wavelength
different from that of the optical signal modulated by the first
light source.
Other aspects, advantages, and salient features of the invention
will become apparent to those skilled in the art from the following
detailed description, which, taken in conjunction with the annexed
drawings, discloses exemplary embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawing(s) will be provided by the Office
upon request and payment of the necessary fee. The above and other
aspects, features and advantages of certain exemplary embodiments
of the present invention will be more apparent from the following
detailed description taken in conjunction with the accompanying
drawings, in which:
FIG. 1 is a block diagram schematically illustrating a
configuration of a conventional wireless visible light
communication system;
FIG. 2 is a graph illustrating a spectrum of an optical wavelength
band used in a conventional wireless visible light communication
system;
FIG. 3 is a block diagram illustrating a configuration of a
wireless visible light communication system according to an
exemplary embodiment of the present invention;
FIG. 4A is a block diagram illustrating a configuration of a
wireless visible light communication system according to an
exemplary embodiment of the present invention;
FIG. 4B is a block diagram illustrating an exemplary configuration
of an optical receiver side shown in FIG. 4A;
FIG. 5 is a chromaticity diagram explaining a wireless visible
light communication system according to an exemplary embodiment of
the present invention;
FIG. 6 is a graph illustrating outputs measured from optical
transmitters according to an exemplary embodiment of the present
invention; and
FIG. 7A and FIG. 7B are graphs explaining a data communication by a
wireless visible light communication system according to an
exemplary embodiment of the present invention.
Throughout the drawings, like reference numerals will be understood
to refer to like parts, components and structures.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The following description with reference to the accompanying
drawings is provided to assist in a comprehensive understanding of
exemplary embodiments of the present invention as defined by the
claims and their equivalents. It includes various specific details
to assist in that understanding but these are to be regarded as
merely exemplary. Accordingly, those of ordinary skill in the art
will recognize that various changes and modifications of the
embodiments described herein can be made without departing from the
scope and spirit of the invention. Also, descriptions of well-known
functions and configurations are omitted for clarity and
conciseness.
FIG. 3 is a block diagram illustrating a configuration of a
wireless visible light communication system according to an
exemplary embodiment of the present invention. A wireless visible
light communication system 200 according to the exemplary
embodiment of the present invention includes optical transmitters
211, 212 and 213, optical receivers 221, 222 and 223, and a
controller 230.
The optical transmitters 211 to 213 generate optical signals having
different colors. Each of the optical transmitters 211 to 213
generates an optical signal having a corresponding color, and
additionally generates rays of light which have substantially the
same color as the optical signal, and have wavelengths different
from that of the optical signal. That is, the optical transmitters
211, 212 and 213 include first light sources 211a, 212a and 213a
for generating a data-modulated optical signal and second light
sources 211b, 212b and 213b for generating light which has a
wavelength different from that of the optical signal generated by
the first light sources 211a, 212a and 213a, within a band of
substantially the same color as that of the optical signal,
respectively.
The wireless visible light communication system 200 uses red, blue
and green light as carriers for optical communication in order to
transmit/receive optical signals in the natural light state. For
example, when the optical transmitter 211a of the optical
transmitters 211a to 213a generates a red light signal 201, the
other optical transmitters 212a and 213a may generate a blue light
signal 202 and a green light signal 203, respectively. The optical
transmitters additionally generate rays of light having
substantially the same colors as the optical signals 201 to 203 and
having wavelengths different from those of the optical signals 201
to 203 such that they can uniformly maintain the light in the
natural light state by adjusting a ratio of the powers of the
optical signals according to colors.
A light emitting diode or the like, which can generate light having
a corresponding color, may be used as the first light sources 211a
to 213a. A direct modulation scheme for direct data modulation or
an external modulation scheme additionally using a separate
external modulator to modulate light generated by the first light
sources 211a to 213a may be applied to the first light sources 211a
to 213a.
Each of the second light sources 211b to 213b generates light
having a corresponding color under the control of the controller,
and may include a light emitting diode, or the like, which can
generate light having substantially the same color as the optical
signal of the corresponding color and having a wavelength different
from that of the optical signal.
The optical receivers 221, 222 and 223 include photoelectric
converters 221a, 222a and 223a for selecting optical signals at
corresponding wavelengths from received light and/or optical
signals and converting the selected optical signals into electrical
signals. The optical receivers 221, 222 and 223 also include data
detectors 221b, 222b and 223b for detecting data from the
electrical signals converted by the photoelectric converters 221a,
222a and 223a, respectively.
The photoelectric converters 221a to 223a include elements, such as
photodiodes, phototransistors, etc., which can convert light into
electrical signals. A band pass filter, a wavelength selective
filter, or an optical filter, which can selectively transmit only
an optical signal at a corresponding wavelength, may be disposed
between each photoelectric converter 221a, 222a or 223a and a
corresponding optical transmitter 211, 212 or 213.
The controller 230 may be connected, through tap filters and the
like, to paths through which data 1 to data 3 are input to the
optical transmitters 211 to 213, in which the controller 230
divides a portion of each data, compares the powers of data 1 to
data 3 with each other, and controls the output powers of the
second light sources 211b to 213b in the optical transmitters 211
to 213.
FIG. 4A is a block diagram illustrating a configuration of a
wireless visible light communication system according to an
exemplary embodiment of the present invention, and FIG. 4B is a
block diagram illustrating a part of an optical receiver side shown
in FIG. 4A. A wireless visible light communication system 300
according to an exemplary embodiment of the present invention
includes optical transmitters 311, 312 and 313 capable of
generating optical signals and rays of light, which have different
colors, optical receivers 321, 322 and 323 for detecting data 1,
data 2 and data 3 from optical signals 301, 302 and 303 having
corresponding colors and wavelengths, respectively, and a
controller 330 for controlling each of the optical transmitters 311
to 313 to maintain light in the natural light state.
Each optical transmitter 311, 312 and 313 includes a first light
source 311a, 312a and 313a for generating a data-modulated optical
signal, and at least one second light sources 311b, 312b and 313b
which generates light having substantially the same color as the
first light source 311a, 312a and 313a and having a wavelength
different from that of the first light source 311a, 312a and 313a
in order to maintain light in the natural light state.
The wireless visible light communication system 300 according to an
exemplary embodiment of the present invention includes the optical
transmitters 311 to 313 which use red, blue and green light as
carriers in order to maintain light in the natural light state.
Therefore, in order to maintain the output powers of the optical
transmitters 311 to 313 at a predetermined ratio, the optical
transmitters 311 to 313 according to the exemplary embodiment of
the present invention further includes separate second light
sources 311b to 313b which generate light having substantially the
same color as each corresponding optical signal and having a
wavelength different from that of the corresponding optical
signal.
The controller 330 detects each portion of data 1 to data 3 input
from an exterior by means of a tap filter or the like, thereby
being able to control each of the second light sources 311b to 313b
by adjusting the ratio of the powers according to the data. The
controller 330 may apply corresponding data to the second light
sources 311b to 313b if necessary.
Each of the optical receivers 321 to 323 includes at least one of
photoelectric converters 321a, 322a, 323a, 321b, 322b and 323b, at
least one of data detectors 321c, 322c, 323c, 321d, 322d and 323d
corresponding to the photoelectric converters 321a, 322a, 323a,
321b, 322b and 323b, respectively, and one of operation units 321e,
322e and 323e connected to the data detectors 321c, 322c, 323c,
321d, 322d and 323d.
An optical filter 324 for selecting a wavelength is disposed
between each of the photoelectric converters 321a 322a, 323a, 321b,
322b, 323b and a corresponding optical transmitter 311 to 313. The
optical filter 324 may include a band pass filter, a wavelength
selective filter and so on.
According to an exemplary embodiment of the present invention, when
data-modulated light is output from the second light sources, the
optical receivers 321 to 323 convert the data-modulated light into
electrical signals by means of corresponding photoelectric
converters 321b to 323b and output the electrical signals to
corresponding data detectors 321d to 323d. The operation units 321e
to 323e can converge data detected by the data detectors 321c to
323c and 321d to 323d.
FIG. 5 is a chromaticity diagram explaining a wireless visible
light communication system according to an exemplary embodiment of
the present invention, in which the chromaticity diagram refers to
a graph obtained through quantification of the distribution of
colors. FIG. 6 is a graph illustrating the outputs measured from
optical transmitters according to an exemplary embodiment of the
present invention, in which each optical transmitter generates
fundamental light having a corresponding color as well as at least
one ray of light having substantially the same color as the
fundamental light and having a wavelength different from that of
the fundamental light.
The chromaticity diagram shown in FIG. 5 refers to colorimetric
rules defined in the general assembly of the Commission
Internationale del'Eclairage (CIE) in 1931.
The chromaticity diagram quantitatively expresses every color with
three factors, i.e., x, y, and Y, on the basis of values measured
by a spectrophotometer. The "Y" is also called a photometric
quantity and represents a value obtained through quantification of
the brightness of color. The "x" and "y" represents a chromaticity
in a pair. The chromaticity represents a color characteristic,
other than the brightness of color, and indicates a point (i.e.,
coordinates) on the chromaticity diagram.
Natural light (or white light) may be implemented through a
combination of three colors, i.e., red, blue and green, in which
the three colors (i.e., red, blue and green) correspond to the
coordinates of R (x.sub.r3, y.sub.r3), G (x.sub.g3, y.sub.g3), B
(x.sub.b3, y.sub.b3) on the chromaticity diagram of FIG. 5.
The R (x.sub.r3, y.sub.r3) represents a sum of two rays of light
having wavelengths of .lamda..sub.R1 (R.sub.1; x.sub.r1, y.sub.r1,
Y.sub.r1) and .lamda..sub.R2 (R.sub.2; x.sub.r2, y.sub.r2,
Y.sub.r2), respectively, in which according to an exemplary
embodiment of the present invention, one of two wavelengths may
correspond to a red light signal (i.e. a data-modulated optical
signal generated from the first light source), and the other
wavelength may correspond to red light (i.e. light generated from
the second light source).
The G (x.sub.g3, y.sub.g3) represents a sum of two rays of light
having wavelengths of .lamda..sub.G1 (G.sub.1; x.sub.g1, y.sub.g1,
Y.sub.g1) and .lamda..sub.G2 (G.sub.2; x.sub.g2, y.sub.g2,
Y.sub.g2), respectively, in which according to an exemplary
embodiment of the present invention, one of two wavelengths may
correspond to a green light signal (i.e. a data-modulated optical
signal output from the first light source), and the other
wavelength may correspond to green light (i.e. light generated from
the second light source in order to maintain light in the natural
light state).
The B (x.sub.b3, y.sub.b3) represents a sum of two rays of light
having wavelengths of .lamda..sub.B1 (B.sub.1; x.sub.b1, y.sub.b1,
Y.sub.b1) and .lamda..sub.B2 (B.sub.2; x.sub.b2, y.sub.b2,
Y.sub.b2), respectively, in which according to an exemplary
embodiment of the present invention, one of two wavelengths may
correspond to a blue light signal (i.e. a data-modulated optical
signal output from the first light source), and the other
wavelength may correspond to blue light (i.e., light generated from
the second light source in order to maintain light in the natural
light state).
One of the optical transmitters according to an exemplary
embodiment of the present invention outputs light corresponding to
the R (x.sub.r3, y.sub.r3) of FIG. 5, and the other optical
transmitters output light corresponding to the G (x.sub.g3,
y.sub.g3) and B (x.sub.b3, y.sub.b3), respectively. That is, in
order to uniformly maintain light in the natural light state by
means of a combination of data-modulated optical signals having
different colors, the wireless visible light communication system
according to an exemplary embodiment of the present invention
generates optical signals having red, blue, and green colors and
rays of light which have substantially the same colors as the
optical signals and have wavelengths different from those of the
optical signals.
The controller according to an exemplary embodiment of the present
invention calculates a ratio of brightness between wavelengths of
each color, as shown in equation (1) below, which can be used to
control the second light sources so as to maintain light
corresponding to the coordinates of R (x.sub.r3, y.sub.r3), G
(x.sub.g3, y.sub.g3) and B (x.sub.b3, y.sub.b3).
.alpha..times..times..times..times..times..times..times..times.
##EQU00001##
Equation 1 represents a ratio .alpha. of powers between two rays of
red light having wavelengths of .lamda..sub.R1 (R.sub.1; x.sub.r1,
y.sub.r1, Y.sub.r1) and .lamda..sub.R2 (R.sub.2; x.sub.r2,
y.sub.r2, Y.sub.r2), in which the ratio may be calculated by color
coordinate values of light according to each wavelength. Equation 1
for red light may be equally applied to green light and blue light,
as well.
Since an optical signal is usually determined according to data to
be modulated, the controller identifies the power of the data, and
can control the total amount of output light by controlling the
second light source according to the identified power.
FIGS. 7A and 7B are graphs explaining a data communication of a
wireless visible light communication system according to an
exemplary embodiment of the present invention, in which an
On-Off-Keying (OOK) modulation scheme is exampled.
FIGS. 7A and 7B illustrate amplitudes of signals output from an
optical transmitter according to an exemplary embodiment of the
present invention. The optical receiver side can determine whether
a received optical signal is at an On level (e.g. 1) or an Off
level (e.g. 0) corresponding to reference values 501 and 508.
Referring to FIG. 7A, it can be understood that there is a section
502, during which no data is transmitted. Also, referring to FIG.
7B, it can be understood that the second light source maintains a
constant state during a section 506, which corresponds to the
section 502 of FIG. 7A during which no data is transmitted.
In contrast, it can be understood that section 507 of FIG. 7B
corresponding to a data transmission section 503 of FIG. 7A
illustrates an inverse amplitude of that shown in the data
transmission section 503. A pattern of amplitudes of light output
upon transmission of an optical signal can be identified from FIGS.
7A and 7B.
As shown in FIG. 7A, the operation units 321e to 323e store a first
reference value 501 for optical signals generated from the first
light sources 311a to 313a and a second reference value 508 for the
second light sources 311b to 313b, and can converge data detected
from the data detectors 321c to 323c and 321d to 323d by comparing
the data with the reference values and compensating the data.
The wireless visible light communication system according to an
exemplary embodiment of the present invention additionally
generates at least one ray of light having the substantially same
color as a data-modulated optical signal and having a wavelength
different from that of the data-modulated optical signal, so that
it is possible to uniformly maintain light in the natural light
state.
Also, the wireless visible light communication system according to
an exemplary embodiment of the present invention can provide
illumination for the user in an indoor environment or the like, and
can minimize fatigue of the eyes of the user.
Certain aspects of the present invention can also be embodied as
computer readable code on a computer readable recording medium. A
computer readable recording medium is any data storage device that
can store data which can be thereafter read by a computer system.
Examples of the computer readable recording medium include
read-only memory (ROM), random-access memory (RAM), CD-ROMs,
magnetic tapes, floppy disks, optical data storage devices, and
carrier waves (such as data transmission through the Internet). The
computer readable recording medium can also be distributed over
network coupled computer systems so that the computer readable code
is stored and executed in a distributed fashion. Also, functional
programs, code, and code segments for accomplishing the present
invention can be easily construed by programmers skilled in the art
to which the present invention pertains.
While the invention has been shown and described with reference to
specific exemplary embodiments thereof, it will be understood by
those skilled in the art that various changes and modifications in
form and details may be made therein without departing from the
spirit and scope of the invention as defined by the appended claims
and their equivalents.
* * * * *